The development codename of an Ubuntu release takes the form "Adjective Animal". Initially these weren't in alphabetic order - until Dapper DRAKE (6.06).
Ubuntu Warty WARTHOG (4.10):
Ubuntu Hoary HEDGEHOG (5.04):
Ubuntu Breezy BADGER (5.10):
Ubuntu Dapper DRAKE (6.06):
Ubuntu Edgy EFT (6.10):
Ubuntu Feisty FAWN (7.04):
Ubuntu Gutsy GIBBON (7.10):
Ubuntu Hardy HERON (8.04):
Ubuntu Intrepid IBEX (8.10):
Ubuntu Jaunty JACKALOPE (9.04):
Ubuntu Karmic KOALA (9.10):
Ubuntu Lucid LYNX (10.04):
Ubuntu Maverick MEERKAT (10.10):
... to be continued.
You can read more about the Ubuntu code names @ Ubuntu wiki